1. FIELD OF THE INVENTION
The present invention relates to an ink jet recording paper.
2. DESCRIPTION OF THE PRIOR ART
Recently, ink jet recording process is rapidly extending in various fields such as hard-copying devices for figures including Chinese characters, and color images, because it has various excellent characteristic advantages such as high copying speed, low noise, easiness to produce multi-color image, applicability to a wide variety of record patterns and unnecessity of development and fixation. Furthermore, application of ink jet recording process to multi-color printing and color photographic printing is also being attempted, because the color image produced by the ink jet recording process is not inferior to the color images produced by usual multi-color printing process and the cost of ink jet recording process is lower than that of conventional printing processes using printing plate or printing master sheet when only a small number of prints are to be made.
Plain papers and coated papers used in the usual printings and the so-called baryta paper used as a base for photographic printing paper are very low in the absorbability of ink. Accordingly, if they are used in the ink jet recording process, the ink remains on the surface of paper for a long period of time, and the remaining ink will stain the image if parts of recording device touches the ink, and if the operator touches the ink or the printed surface is rubbed by the continuously discharged sheet. Further, if ink droplets of 2-4 colors are superposed at one position in high density images or multi-color records, the large quantity of inks remaining unabsorbed mix themselves together or the inks flow out of the position. Thus, these papers are practically unusable for the ink jet recording process.
The paper for use in the ink jet recording process must give an image of high color density and clear color tone. In addition, it must rapidly absorb the ink and must be free from the flow-out of ink and from the danger of stain even if the paper is touched just after printing. In addition, the diffusion of ink dot to the lateral direction on the recording sheet must be prevented in order to give an image free from blurring and having a high resolution. The paper for ink jet recording process must satisfy all these requirements simultaneously.
Hitherto, various proposals have been made with the aim of solving these problems. For example, there is mentioned in Japanese Patent Kokai (Laid-Open) No. 53,012/77 an ink jet recording paper prepared by wetting a low-sizing base paper with a coating material for surface treatment. In Japanese Patent Kokai (Laid-Open) No. 49,113/78, there is disclosed an ink jet recording paper prepared by impregnating a sheet internally containing powdery urea-formaldehyde resin with a water-soluble polymer. In Japanese Patent Kokai (Laid-Open) No. 5,830/80, there is disclosed an ink jet recording paper prepared by providing an ink-absorbing layer coated on the surface of a support. In Japanese Patent Kokai (Laid-Open) No. 51,583/80, there is disclosed a case in which a non-colloidal substance is used as the pigment in coated layer. In Japanese Patent Kokai (Laid-Open) No. 146,786/80, there is disclosed an ink jet recording paper having a water-soluble polymer-coated layer. Further, in Japanese Patent Kokai (Laid-Open) No. 11,829/80, there is disclosed a method for controlling the spreading of ink dot and speed of ink absorption by using a structure having 2 or more layers in which the ink-absorbability of the uppermost layer is adjusted to 1.5-5.5 mm/minute and that of the second layer is adjusted to 5.5-60.0 mm/minute.
However, in the technical ideas represented by Japanese Patent Kokai (Laid-Open) No. 58,012/77, it is intended to enhance the degree of resolution by sacrificing the ink-absorbability to some extent. On the other hand, the technical ideas represented by Japanese Patent Kokai (Laid-Open) No. 49,113/78 have a defect that the ink is diffused deeply into the paper layer so that the ink cannot produce a high color density, even though considerably high ink-absorbability and resolution can be reached. Thus, both the techniques are unsatisfactory as multi-color ink jet recording paper.
As a method for overcoming the above-mentioned defects, an ink jet recording paper coated with non-colloidal silica powder has been disclosed in Japanese Patent Kokai (Laid-Open) No. 51,583/80 and OMR (optical mark reader) papers such as bar code printing paper, coated with finely powdered silicic acid, have been disclosed in Japanese Patent Publication No. 790/78.
Although resolution, color property, color density, absorbability, roundness of printed dot image and the like can be greatly improved by providing a surface layer of synthetic silica or other white-colored fine powder as above, such papers are still unsatisfactory when used as a poster exposed outdoors or a photograph to be stored for a long period of time, because many of the inks applied to these papers are water-soluble so that the ink will dissolve out again if the image formed thereon is contacted with water.
In order to solve this problem, a variety of proposals have been made hitherto. For example, in Japanese Patent Kokai (Laid-Open) No. 53,591/80, there is disclosed a recording paper in which a water-soluble metal salt is attached to the recording surface. In Japanese Patent Kokai (Laid-Open) No. 84,992/81, there is disclosed an ink jet recording process which comprises printing images on a recording medium containing a polycationic polyelectrolyte in its surface with an aqueous ink containing a water-soluble direct dye or acid dye. In Japanese Patent Kokai (Laid-Open) No. 150,396/80, there is disclosed a method for enhancing the water-resistance of an ink jet record which comprises, after an ink jet recording by the use of an aqueous ink, treating the record with a waterproofing agent capable of forming a lake with the dye in the aqueous ink. In Japanese Patent Kokai (Laid-Open) No. 58,869/81, there is disclosed a method for enhancing the water-resistance of ink jet recording sheet which comprises, after making an ink jet record with an aqueous ink on an ink jet recording sheet coated with a water-soluble polymer, treating the sheet with a waterproofing agent capable of insolubilizing the water-soluble polymer.
Sometimes, various cation resins are used as the waterproofing agent for the image produced from aqueous ink, and as the cation resin, mordants such as dicyandiamide condensate, polyamines, polyethyleneimine and the like have been used. However, if the mordant is used in so large an amount as to obtain a sufficient water-resistance, the white-colored paper can yellow in the air or upon irradiation by sunlight or, even if the yellowing of white-colored paper does not take place, the sunlight-fastness (sunlight-stability) of the dye constituting the image is deteriorated. Thus, it has been quite difficult to fulfil both the requirements concerning water-resistance and weather-stability (resistance to yellowing of sheet and light stability of image).